20 May 2013

Atmospheric and terrestrial water storage changes have made only a “minor” contribution

Around 2005, accelerated melting of polar ice sheet and mountain glaciers, together with rising sea level, caused the North Pole to drift towards east, marking an “abrupt departure” from the direction recorded over the past century. Accelerated rates of ice melting in Greenland and Antarctica have been observed since 2005-2006 and thus coincide with the abrupt change in polar shift.

“When mass is lost in one part of a spinning sphere, its spin axis will tilt directly towards the position of the loss,” Erik Ivins, a geophysicist at NASA’s Jet Propulsion Laboratory in Pasadena, California was quoted as saying in Nature.

The melting ice has also increased the rate of drift from about two milliarcseconds (MAS) per year during the period 1982-2005 to about nine MAS per year post 2005, a study published recently in theGeophysical Research Letters journal states.

The changes were recorded by satellite gravity measurements by the Gravity Recovery and Climate Experiment (GRACE) mission, jointly sponsored by U.S. and Germany.

GRACE provides monthly gravity field data that correlates with mass changes for the entire Earth, and from this, it is possible to extract the precise contributions from individual sources. This information helped the scientists in pinning down the cause of abrupt pole drift in 2005 to “variations in climate system”.

Atmospheric and terrestrial water storage changes have made only a “minor” contribution to the shift in Pole direction and rate. The researchers from the University of Texas at Austin consider this study as a reaffirmation of the increased ice melting at poles and mountain glaciers in recent years. This is borne from the fact that mass movement in solid earth takes place over long time scales.

Since earth monitoring using satellites has begun only during the last few years, there is no way of knowing the rate and amount of ice-sheet melting in the past. However, data on polar motion is available, thus making it possible to extrapolate the polar ice-sheet melting in the past.